Heart tachyarrhythmias, including fibrillation, in a patient can be stopped by applying an electrical pulse to the patient, such as with a defibrillator. In general, defibrillators have comprised an electrical energy source and a pair of electrodes connected to the energy source with an electromechanical relay switch. The electrodes are placed in contact with the patient's chest, and the relay switch closed to deliver a high energy pulse to the patient. Prior defibrillators of this type suffer the disadvantage that the electromechanical relay switch has a comparatively slow switching time, and is subject to contact chatter.
In U.S. Pat. No. 3,773,050, Panico discloses using a gas-filled discharge flash tube as a fast acting, high energy switch in a defibrillator. The flash tube is non-conducting until a triggering pulse is applied to its control electrode. The flash tube then continues to conduct until electrical energy from a power source is discharged through the flash tube and patient to a particular voltage.
For effective heart defibrillation, application of a relatively precise amount of electrical energy to the patient can prove critical. Certain types of defibrillation pulse wave forms have also proven to be more beneficial. The ANSI/AAMI DF2-1989 standard provides specifications for two defibrillation pulse wave forms, a damped sinusoidal wave form and a truncated exponential wave form. The damped sinusoidal wave form is generally obtained by discharging a capacitor through a waveshaping inductor. The truncated exponential wave form is generally obtained by truncating a capacitor discharge. These wave forms have been proven in clinical studies to be highly effective in terminating heart fibrillations.
U.S. Pat. No. 4,823,796 to Benson, which is incorporated herein in its entirety by reference, is an example of a known defibrillator which delivers a truncated exponential or trapezoidal defibrillation pulse to a patient.